Automatic telephone system



B. p. WILLIS.

AUTOMATIC TELEPHONE SYSTEM. APPLICATION FILED MAR. 29. 1920.

1,376,848. Patented ay 3,1921.

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UNITED STA'iiLA'lENT orrics.

BERNARD D. WILLIS, or OAK PARK, ILLINOIS, ASSIGNOR 'ro AUTOMATIC ELECTRIC" COMPANY, OF CHICAGO, ILLINOIS, A CORPORATTON OF ILLINOIS.

AUTOMATIC TELEPHONE SYSTEM.

-- Patented Ma 3, 1921.

Application filed March 29, 1920. Serial No. scam. 1 p

ed certain new and useful Improvements in Automatic Telephone Systems, of which the following is a specification. 7

My invention relates in general to automatic telephone systems in which automatic switching mechanism is employed at a central exchange for completing connections; and the object of the invention is to provide the direction of current flow in a calling telephone line upon the response of the called subscriber, the principal effect of my improvement being to eliminate to a great I extent the disagreeable click or bang heretofore produced in the receiver at the calling station. There are also other advantages incidentally obtained which will be mentioned later.

In all modern automatic systems there are a number of features or specialservices incident to successful operation which are controlled in some way by the response of the called subscriber. Chief among these 7 may be mentioned measured service, including meter service and paystation service or coin collect,-and supervision to calling operators. While a number of circuit arrangements havebeen devised to take care of these features, the most successful and the one in almost universal use at the present time is the so-called reverse battery method. .Means is provided at the switch ing mechanism from which talking battery is supplied to the calling line, generally the connector switch, or a repeater in a multiofiice system, whereby the flow of current in the calling line is reversed when the called man answers. The following-issued U. S; Patents will serve toillustrate the art. Willis, No, 1,156,450, granted Oct. '12, 1915.

-Martin, No. 1,316,101, granted Sept. 16,

Ray, No. 1,804,369, granted May 20, 1919. Erickson, No. 1,225,603, granted May 8, 1917.

It is the custom at the present time to provide all connector switches and repeaters with the reversing means, at least this is done in all systems of any great size, and the means used heretofore consists of a make before break spring combination mounted on the back bridge relay, or other relay controlled thereby, whosefunction it is to re verse incoming line conductors as regards their connections to the windings of the line relay. lVhile this device operates satisfacto' 'r1ly so far as merely reversing the'current is r I concerned, it has the great-disadvantage of producing a loud and annoying click or hang in the receiver at the calling station when the current is reversed. My invention does awaywith this disagreeable noise almost entirely, in a manner and through means which will now be explained.

Referring to the drawing, I have shown in skeleton diagram, all unnecessary parts being omitted, a complete circuit connection between acalling station A and a called station'A. in a system embodying my inven A The connection is assumed to have been established by means of an individual line switch or trunk selector, indicated by reference characterC; one or moreselector tion.

switches, one of which is indicated by the reference character D; and a connector switch, indicated by reference character I-I. It is in the latter switch that the special reversing arrangement inwhich the invention lies is located.

The drawing 1s exceeding simple and the operation will doubtless be obvious, but it will be explained briefly; Relays 4 and 5 are the usual line and release relays, relay 2 is the back bridge relay, while 3 is a special'battery feed relay provided in accordance with my invention. The line conductors incoming to the connector Hnormally terminate in the windings of the linerelay 4, and this relay controls the operation of the connector in the ordinary manner. When the receiver is removed at the called with the result that thefincoming line conductors are disconnected {from the windings of the line relay 4 and are connected instead to the windings of the special battery 7 station the back bridge relay 2 is energized feed relay 3; or in other words, relay 3 is substituted for relay 4 in the circuit of the.

calling line. It will be noticed that the'upper line conductor is by this operationshifted from battery to ground, while the lower line conductor'is shifted from ground to battery, the result being that the direction of current flow is reversed in the calling line. Relay 8 has a pair of contact springs which close an auxiliary energizing circuit for the release relay 5 in order to maintain this relay energized after the line relay 4:.

has fallen back.

A complete discussion of the current flow in the calling line during reversal will not be attempted, as it is somewhat complicated, but it may be stated that the elimination of the bang in the receiver at the calling station is principally due to the fact'that the relay 3 is connected to the line in deenergized condition. When relay 2 energizes, the current in the line falls to zero quite rapidly, the two sides of the line being connected to points of approximately equal potential as soon as the armatures of relay 2 engage their respective working contacts. This condition, in which relays 3 and l are connected in series, exists only for a very small fraction of a second and the period is so short I that the magnetism in relay 8 does not build up to any great extent. When relay at is disconnected by the further movement of the armatures,the current in the calling line rises gradually because of the impedance of relay 3 and the effect in the receiver is correspondingly modified, the annoying bang being almost entirely eliminated. This result willbe readily comprehended if the I and only fairly efiicient as a retard coil.

above described reversing operation is contrasted with the old method in'which the there is nothing to oppose the sudden change. An additional advantage secured by my nnproved reversing arrangement w1ll now be pointed out. The line relay 4L may be of relatively low impedance and designed for a maximum efficiency in responding to impulses, while the battery feed relay 3 may be of very high impedance designed to produce a talking circuit of, maximum efiiciency. Heretofore, where the line relay was used to supply talking battery to the calling line it was necessary to design this line relay on a sort of a compromise basis, the result being a relay only fairly eflicient as a line relay y my arrangement, in which separate relays are provided to takeof these diiferent functions,-each relaymay be designed with special reference to the work it has to perform,

' thus securing a maximum efliciency both in in the appended claims.

lVhat I claim as my invention is: p

1. In a telephone system, an automatic connector switch, a line relay in said switch controllable over the two sides of a calling line in series to operate said switch to con nect with a called line, a battery feed relay in said switch, and means operated upon the response of the called subscriber to substitute said battery feed relay for said line relay in the circuit of the calling line, the connections being such that the direction of current flow in the calling line is reversed. V

2. In a telephone system, means for connecting a calling and called line including an automatic connector switch, a line relay in said switch controllable over the two sides of the calling line in series to operate said switch, and means for reversing the direction of current flow in the calling line when the called subscriber answers, said means comprising a battery feed relay normally deenergized, and arelay controlled over the called line to substitute said battery feed relay for the said line relay in the circuit of the calling line.

3. In a telephone system, means including an automatic switching mechanism for connecting a calling and called line, a line relay controlled over the two sides of the calling line in series to control the operation of said mechanism, and means for reversing the di rection of current flow in the calling line when the called subscriber answers, said means comprising a second relay normally deenergized, and a relay controlled by the called subscriber to substitute said second relay for said line relay in the circuit 'of the calling line. e i

4:. In a telephone system, means including an automatic switching mechanismfor connecting a calling and called line, a line relay energized over the two sides of the calling line in series for controlling the operation of said mechanism, .means for reversing the direction of current flow in the calling line when the called subscriber answers, and means for accomplishing the reversal without disturbance in the receiver at the calling station, said means including a normally deenergized relay through which current is v supplied to the calling'line after reversal thereof, the impedance of said last relay bemg effective to cause a gradual rise of ourrent in the calling line in the reverse direc- .tion.

connecting a calling and called line, a line relay controlled over the two sides of the calling lin in series to control the operation of said mechanism, said relay being of relatively low impedance, a battery feed relay of high impedance, means for substituting said battery feed relay for said line relay when the called subscriber answers, and circuit connections such that the direction of current flow in the calling line is reversed when the substitution takes place.

7 In a telephone system, means including an automatic switching mechanism for connecting a calling and called line, a double wound line relay controlled over the two sides of the calling line in series for controlling the operation of said- 'mecha nism, the two windings of said relay being connected in bridge of the calling line in series with the exchange battery, a relay 7 for reversing the direction of current flow in the calling line after the said switching mechanism has been operated, and means for minimizing the effect of the current reversal on the receiver at the calling station, said means including a pair of normally deenergized inductive windings which are substituted for the windings of the said line relay when the current is reversed, the impedance of said inductive windings being effective to cause a gradual ris of current in the calling line in thereverse direction.

8. In a telephone system, means including an automatic switching mechanism for connecting a calling and a called line,1a line relay controlled over the two sides of the callingline in series to control the operation of said mechanism, said relay being of low impedance, a slow acting release relay for controlling the release of said mecha nism, a circuit for said release relay closed by said line relay when energized, a battery feed relay of relatively high impedance,

means for substituting said battery feed relay for said line relay to supply talking current to the calling line during conversation, circuit connections such that the direction of current flow in the calling line is reversed when the substitution takes place, and a new circuit for said release relay closed by said battery feed relay to maintain the release relay energized after the line relay has denergized.

Signed by me at Illinois, this 25th day of March, 1920.

BERNARD D. WILLIS.

Chicago, Cook county, 

